In ultrafast optics, optical parametric amplification serves to extend the capabilities of ultrashort laser light pulse sources to higher peak powers, higher average powers and new wavelengths. In recent years, efforts to develop optical parametric amplification have produced gain bandwidths supporting direct amplification of few-cycle pulses (i.e., with pulse durations under five cycles) at several wavelengths in the near- and mid-infrared, usually employing beta barium borate (β-BaB2O4) or periodically-poled lithium niobate (PPLN), and in one or two instances approaching two-cycle pulse amplification with spectra covering about ⅔ of an octave. However, an octave-spanning spectrum has never been amplified before, due to the unavailability of nonlinear materials and phase-matching techniques with sufficiently broad phase-matching bandwidth.
Meanwhile, the extension of optical parametric amplification to high-repetition-rate systems is a major challenge and a heavily sought-after result. In nonlinear spectroscopy, higher repetition rates would yield faster measurement times and higher signal levels. For frequency metrology, high repetition rates are important for many applications, including astronomy and signal interrogation. Furthermore, high-harmonic generation driven by high-repetition rate, high-average power, few-cycle optical-parametric-amplification sources would present a major step forward for attosecond science by enabling an increase in obtainable photon flux. Optical parametric amplification, however, is traditionally limited to repetition rates low enough that the pulse energy of the pump source can exceed a threshold of approximately 10 μl, thus allowing enough gain in a feasible geometry. For this reason, parametric amplifiers are normally pumped by amplified lasers with kHz and lower repetition rates. While recent developments in high-average-power amplifiers and oscillators have led to optical-parametric-amplification systems with repetition rates as a high as a few MHz, multi-kW average power pump lasers, with high cost and complexity, are thought to be necessary to push parametric amplifier repetition rates towards 100 MHz and higher with the previous optical-parametric-amplification systems.
The use of optical parametric amplification is suitable for a range of wavelengths and is further described, for example, in R. A. Baumgartner, et al., “Optical Parametric Amplification,” IEEE J. Quantum Electron QE-15, 432-444 (1979) and in G. Cerullo, et al., “Ultrafast Optical Parametric Amplification,” Rev. of Sci. Instrum 71 1 (2003). Application of the well-known chirped-pulse-amplification technique to parametric amplification was developed in the early 1990's. See A. Dubietis, et al., “Powerful Femtosecond Pulse Generation by Chirped and Stretched Pulse Parametric Amplification in BBO Crystal,” Opt. Commun. 88, 433-440 (1992). This so-called parametric chirped-pulse amplification (P-CPA) received attention, for example in J. Collier, et al., “Evaluation of an Ultrabroadband High-Gain Amplification Technique for Chirped Pulse Amplification Facilities,” Appl. Opt. 38, 7486-7493 (1999) and in I. Jovanovic, et al., “Optical Parametric Chirped-Pulse Amplifier as an Alternative to Ti:Sapphire Regenerative Amplifiers,” Appl. Opt. 41, 2923-2929 (2002).
Cavity-enhanced optical parametric amplification is also discussed in U.S. Pat. No. 7,405,868 B2, in which present inventor, Franz Kaertner, was also named as an inventor.